The present invention relates to a gain control integrated circuit and, more particularly, to a variable resistance gain control integrated circuit used for the automatic gain control power stage of a television video signal amplifying system.
In a variable resistance gain control integrated circuit of this type, resistors are connected to the emitters of two transistors constituting a differential pair, and a further two transistors are inserted as an active load. By changing a gain control current source connected to the two transistors serving as the active load, saturation resistances thereof can be varied. As a result, emitter resistances of the two transistors serving as the differential pair change, to effect gain control of the circuit.
The integrated circuit of this type generally consists of two transistors serving as a differential pair, another two transistors serving as an active load, and several resistors. Conventionally, the four transistors are formed in different semiconductor island regions, respectively, and the remaining resistors are combined in a single semiconductor island region. However, such a plurality of isolated semiconductor island regions does not allow for appreciable reduction in pattern area.